If there is no share service box, may be the service is not installed.
In control Panel -> Network and Dial-up Connections ->
Right click on the LocalNetwork Icon and select properties.
See if there is a "File And Printer Sharing for Microdof Networks"
If you can't locate it - Click Install and install it....
(You need both PC to be under 1 Subnet mask and IP range)
In the same window, double click "Internet Protocl(TCP/IP)
and add IP address like 192.168.0.1 subMask 255.255.255.0
Do same with the second PC but for it set IP 192.168.0.2 SubMask
255.255.255.0
(This is if there is no DHCP Server which to asign IP to the PCs)
After this changes restart both PCs
this should work
What is strange for me is that you no need WireLess Router to share Files.
Unless the router have 3-4 ports for LocalNet in the back and
you can use it like switch...